Have to color gum paste black and have chefmaster black gel..can I use that? Help!!!In the middle of decorating a cake!

the best way to get black fondant is by using chocolate fondant or if you can dye your fondant brown first. once you get it brown or darker brown then start adding black to the brown fondant, it will be much easier to get black by starting with brown. other wise you may need to use way tooo much black dye since it will only be grey for a very long time until you use up all your black dye.
same trick with butter cream frosting or any other type if you want black, start with chocolate frosting or brown frosting. much easier and less black dye/color that way

Yes, you can use your gel to color gumpaste! That's all that I use! I don't know of any other way to color it. You will have to use a lot of black.